Vacuum tube circuits



Aug. 21, 1934'. R. M. WILMOTTE 1,971,089

' VACUUM TUBE CIRCUITS Filed Aug. 28, 1930 whwmlmmh Patented Aug. 21, 1934 1,971,0 9 VACUUM TUBE omom'rs 'Raymond M. Wilmette, Boonton, N. JJ, assignor, by mcsne assignments, to Radio Corporation of America, New York, N. Y., a. corporation of Delaware Application August 28, 1930, Serial No. 478,416

5 Claims.

. This invention relates to vacuum'tube circuits, and particularlyto a regenerative circuit.

It is well known that'any adjustment of the regeneration control of a tuned amplifier or detector stage results in a detuning of tuned circult. Various arrangements have been proposed to eliminate or reduce this detuning effect but, so far as I am aware, such prior circuit arrangements have failed to render the tuning adjust ment of the input circuit independent of the reen'eraton control.

; In receivers of the type including a plurality of stages .of;.tuned radio frequency amplification, it has been found that the introducticniof regeneration in the-detector stage will eifect such detuning of the input circuit of that stage as to materially reduce the sensitivity when a gang condenser or variometer is employed for the simultaneous tuning of all stages.

Objects of the present invention are to provide methods of and circuit arrangements for controlling regeneration without affecting the frequency adjustment of the input and/or output circuits of the vacuum tube. Further objects are to provide vacuum tube amplifier or detector stages in which regeneration is controlled by a negative resistance circuit coupled to the tuned input circuit of the stages.

These and other objects of the invention will be apparent from the following specification, when taken with the accompanying drawing, in which Fig. 1 is a fragmentary circuit diagram of a radio receiver embodying the invention, and

Fig. 2 is a curve sheet indicating the regeneration control which is possible in such a circuit.

In the drawing, the reference numerals l, 1 indicate radio frequency amplifier tubes working into the detector tube 2; each stage having substantially identical tuned input circuits comprising inductances 3 and adjustable condensers a. As is customary, all of the condenser rotors are coupled mechanically by a shaft 5 to insure the simultaneous adjustment of all of the condensers. The construction, so far as described, is typical of radio receivers employing tuned radio frequency amplification.

In accordance with the present invention, regeneration is controlled by regulating the eifective resistance of the tuned input circuit of the detector tube 2. The plate inductance 6 of a negative resistance vacuum tube or dynatron '7 is closely coupled to the inductance 3 of the detector input circuit, preferably by winding the inductance 6 turn for turn along the inductance 3. The positive potential applied to the outer grid G2 by a battery 8 orcther appropriate current supply is substantially greater than the positive potential impressed uponthe plate P. The tube *7 is illustrated as a tetrode with a negative potential applied to the grid G1 by a current source 9, but it will be apparent that the dynatron 7 may be of the triode, pentode or other appropriate type. H

Due to the close coupling between the. dynatron plate inductance 6 and the inductance 3 of the detector stage, the effective resistance of the detector input circuit is determined by the characteristics ofithe dynatron circuit. It is well known that the operation of a dynatron or nega tive resistance circuit may be controlled in a number of ways, for example, by adjusting the voltage impressed upon one or more of the tube circuits, or by leaving the source voltages fixed and varying a resistance or reactance in one or more of the tube circuits. As indicated in Fig. 1, the plate circuit connection to the current source 8 is provided by a tap 11 which may be adjusted to control the plate potential. While not essential, it is preferable to supply both the plate and the adjacent grid potentials from the same source, as such a system provides energizing potentials of the proper ratio even though their absolute values may vary somewhat from their intended magnitudes.

The effect of the dynatron circuit upon the receiver action is indicated by curve A of Fig. 2 which shows the variation of amplification with dynatron plate voltage. The non-regenerative gain or amplification of the receiver was taken as unity on a logarithmetric system of ordinates and the abscissae represent applied plate voltages, the outer grid G2 having a constant positive potential of 135 volts and the innor grid G1 having a constant negative bias of 10 volts. It will be noted that for approximately 6.2 volts on the dynatron plate, the receiver operated in its normal manner as a non-regenerative receiver and that a regenerative gain was introduced by increasing the dynatron plate voltage. At about 8 volts upon the plate, the resistance of the detector input circuit was reduced to such a point that the detector stage oscillated. Within the range of applied potentials corresponding to a positive slope for the characteristic curve of the dynatron, a positive resistance is introduced into the detector input circuit and the receiver gain falls below its normal non-regenerative value. This method of controlling the gain reduces the selectivity of a tuned amplifier but, for some purposes, this feature is not objectionable.

Careful tests of a receiver embodying the invention have demonstrated that there is no appreciable detuning of the regenerative stage. When the regeneration was introduced by the usual feed-back methods, it was always necessary to adjust the tuned circuit of the regenerative stage. Except for the additional capacity introduced into the tuned circuit of the receiver by the dynatron plate coil, the dynatron circuit has no effect upon the frequency adjustment of the receiver circuit. This introduction of a small capacity may be compensated in the initial alinement of the sections of the gang condenser.

Receivers of the general type illustrated in Fig. 1 may be employed for the reception of modulated carrier waves or interrupted continuous waves. It is to be understood, however, that the invention is not limited to this use with cascaded tuned circuits but affords a general method for controlling the resistance of a tuned circuit without disturbing the frequency adjustment of that circuit.

I claim:

1. The combination with a vacuum tube stage circuit capable of being adjusted so as to produce either a negative or a positive resistance tuned circuit, of a dynatron having a means for coupling said dynatron circuit to said tuned circuit, and means for controlling the operation of said dynatron whereby the amplifying characteristics of said vacuum tube stage may be varied without affecting the tuning of said tuned circuit.

2. The combination with a vacuum tube having a tuned input circuit, of a dynatron circuit having an inductance in the plate circuit thereof, said inductance being coupled magnetically to said tuned circuit, and means for controlling the operation of said dynatron whereby the amplifying characteristics of said vacuum tube may be varied without affecting the tuning of said tuned circuit.

3. The combination with a vacuum tube detector having a tuned input circuit, of a dynatron circuit having a plate circuit impedance coupled to said tuned input circuit, and means for controlling the operation of said dynatron whereby the characteristics of said vacuum tube stage may be varied without afiecting the tuning of said tuned circuit.

4. In an electrical transmission system, a plurality of cascaded vacuum tube stages having tuned input circuits, means mechanically coupling the variable elements of said tuned circuits to effect simultaneous and equal adjustments thereof, a dynatron circuit including a plate impedance coupled to one of said input circuits, and means for controlling the operation of said dynatron.

5. The combination with a vacuum tube stage having a tuned input circuit, of means for controlling the amplification of said stage without disturbing the frequency adjustment of said tuned circuit, said means comprising a dynatron circuit including a plate circuit inductance closely coupled to the inductance of said tuned circuit.

RAYMOND M. WILMOTTE. 

